This invention relates to video image processing, and more particularly to the derivation and assignation of motion vectors indicating the direction and magnitude of current movement to different regions of a video image, in order to assist the generation of desired output images.
Our United Kingdom Patent No. GB-B-2188510 describes a method of producing a list of motion vectors which are applicable over the whole area of a video image and for assigning an appropriate one of the motion vectors in the list to each region of the image. Other methods are possible for generating such lists of motion vectors. The regions to which the vectors are applied may be as small as an individual picture element (pixel) or may comprise a plurality of pixels i.e. a block of the picture.
Such motion vectors are particularly useful when it is desired to generate output video fields which correspond to an instant in time intermediate of two input fields. Such output fields are necessary in video image processing systems which transfer video images to or from film, in standards conversion, or in producing slow notion effects.
In all such applications it is desirable to produce a sharp smoothly moving picture. In the case of slow motion generation, if the technique is used with, for example, a shuttered CCD camera then pictures can be generated with a quality which approaches that obtainable from a high frame rate camera. One possible technique for generating the list of motion vectors and then assigning them to individual picture elements has been proposed in our International Patent Application No. WO-A-9205662 and also in our International Patent Application No. PCT/GB91/01622. This technique is known as the four field algorithm and uses a total of four input fields for assignment of an output vector field. It has been found that for certain types of motion and in particular rotational motion this type of system does not always produce satisfactory results.
Another prior art system is described in British Patent Application No. GB-A-2231743. In this a list of trial vectors is derived using a block matching technique between a pair of fields designated F.sub.1 and F.sub.2. This list or menu of vectors is then applied across a three field interval F.sub.1 to F.sub.4 in order to create a vector field at the instant in time of a desired output vector field. This technique also has problems because vectors are assigned at the output vector field without necessarily taking account of whether or not an object represented by that vector is present in both of the adjacent fields. Thus errors in outputs fields can occur. Also, when the next interval is used (F.sub.2 to F.sub.3) a new set of vectors has to be derived for F.sub.2 and subsequently assigned. This leads to extra calculation and an increase in complexity.